FIGURE 7.

[³H]AziPm photolabels β3Met-227 in βM1. ³H (●, ○) and PTH-derivatives (□, ▵) released during sequencing of fragments isolated by rpHPLC (Fig. 4A, fractions 27–29) from EndoLys-C digests of β3. The primary sequence began at β3Arg-216 near the N terminus of βM1 (□, I₀ = 70 pmol, both conditions), with a secondary sequence beginning at β3Ala-280 before βM3 (▵, I₀ = 18 pmol, both conditions). The peak of ³H release in cycle 12 indicated photolabeling of β3Met-227 in βM1 (−PPF/+PPF, 18/3 cpm/pmol). Inset, direct sequencing of an EndoGlu-C digest of photolabeled β3_{59 kDa}, with OPA treatment in cycle 16 to chemically isolate during further sequencing the fragment beginning at β3His-191 (25 pmol) that contains β3Pro-206 in cycle 16 and extends through βM1. The peak of ³H release in cycle 37 confirmed photolabeling of β3Met-227 (18 cpm/pmol, −PPF).